This invention relates generally to a system and method for detecting terminal shorts. More specifically, this invention relates to a system and method for detecting a terminal-to-terminal short and/or a terminal-to-ground short in a write head.
In conventional rotating disk data storage devices, one or more read/write heads, typically magneto resistive and inductive heads, respectively, including positive and negative terminals, are used to write data on and read data from an associated disk media surface. Such an arrangement is shown in FIG. 1 in which a disk assembly 100 is connected to a host system, a memory, e.g., a RAM 160, and a CPU 170 via an interface adaptor 150. The host system supplies control signals and data to be written to the disk assembly 100 and receives read data from the disk assembly 100 via the interface adaptor 150. The CPU 170 controls, e.g., basic disk drive functions, based on information stored in the RAM 160.
The disk assembly 100 includes a preamplifier 30 supplied voltage by a positive voltage supply and connected to the heads 20 via flexible attachments 25. The preamplifier 30 receives from an associated channel device 40 both data signals to be written onto a disk 10 during a write operation, as well as control signals used to specify the individual read/write head 20 to be selected for a read or write operation. Data is supplied to the channel device 40 via a controller 50 connected to the interface adaptor 150. The preamplifier 30 also typically supplies analog data signals read from the head 20 to the associated channel device 40. A spindle motor 80 rotates the disks 10 under the control of a spindle motor controller 90. An actuator motor, e.g., a voice coil motor 60, moves the heads 20 to tracks at different radial positions on the disks 10 under the control of a position system 70 in response to control signals from the channel device 40.
The manufacture of disk drive assemblies is becoming more complex as additional read/write heads and corresponding additional disks are being included. Chances for assembly error are high since the heads and flexible attachments are often supplied by multiple sources in an effort to meet critical production quotas and schedules. Defects can occur during assembly due to, e.g., soldering across terminals, bent flexible attachments, etc. These defects can result in terminal-to-terminal shorts that can result in lost data or can cause terminal-to-ground shorts that can cause excessive currents that can damage the sensitive read/write heads as well as the preamplifier and will also result in lost data. Disk drive yield and manufacturing expenses can be improved if circuits for detecting head assembly defects can be included in the preamplifier.
Fault detection devices are known. For example, U.S. Pat. No. 5,081,404 discloses a motor driver fault detection circuit that measures a motor short-to-ground or short-to-supply voltage by directly monitoring the motor terminal voltages.
Devices are also known for detecting excessive currents in drivers when a short-to-ground occurs. For example, U.S. Pat. No. 5,773,991 discloses a motor current sensing circuit that includes a mirrored H-bridge driver that mirrors current from the actual driver. Current is sensed by measuring the voltage across a resistor that takes the place of the motor in the mirrored driver. U.S. Pat. No. 5,483,404 describes a method for over current detection in an H-bridge motor driver. This circuit senses a differential voltage across a resistor in series between a positive supply and an H-bridge driver.
If conventional designs such as these were employed for sensing a short-to-ground in a write head, a high current output from the positive voltage supply connected to the driver might cause the driver to saturate, though the current may not be due to a short but may, instead, be merely a high write current. Thus, using such designs may impede driver performance.
There is thus a need for a technique for detecting write head terminal-to-terminal shorts and terminal-to-ground shorts to avoid the loss of data, without impeding the performance of a write head driver.
It is therefore an object of this invention to provide a system and method for detecting write head terminal-to-ground shorts and terminal-to-terminal shorts that will avoid the loss of data without impeding the performance of the write head driver.
According to exemplary embodiment, these and other objects are met by a system and method for detecting shorts in terminals fed current by a driver connected to the terminals.
According to a first embodiment, at least one virtual driver is connected to the driver for processing an output of the driver. A detector detects if a short has occurred, based on an output of the virtual driver. For this purpose, the detector detects when an output of the virtual driver exceeds a first threshold. If the detector detects that the output of the virtual driver has exceeded the first threshold, this indicates a terminal-to-ground short. The shorts may be detected in terminals in one or more write heads. The driver, virtual driver, and detector may be included in a preamplifier. Detecting shorts in this manner avoids saturation of the driver due to high write current and avoids the loss of data.
According to a second embodiment, a detector detects if a short has occurred, based on an output of the driver. For this purpose, the detector detects when an output of the driver drops below a second threshold. If the detector detects that the output of the driver has dropped below the second threshold, this indicates a terminal-to-terminal short. These shorts may be detected in terminals in one or more write heads. The driver and detector may be included in a preamplifier. Detecting shorts in this manner avoids the loss of data.